The present invention relates to a device for generating variable voltage of the type in which a voltage across a non-polarized capacitor inserted between the gate of a MOS field-effect transistor and the ground is controlled in response to a positive or negative input selectively switched by two switching elements which in turn are controlled in response to small DC control signals, so that the output voltage derived from the source of the field-effect transistor may be varied continuously.
In general, variable resistors are widely used in order to vary output voltages, but they have an objectionable feature in that noise is produced because the slider or armature slides over a resistor so as to vary the voltage. Furthermore they have another objectionable feature in that the output voltages are unstable because the characteristics of the resistors tend to change very easily in response to the environmental temperature.